A wireless power transfer system may include a wireless power transmitter unit (PTU) and a wireless power receiving unit (PRU). A PRU may be implemented in a mobile computing device, such as a laptop, tablet or smart phone, which can be placed on a charging mat equipped with a PTU. The PTU may include a transmit (Tx) coil and the PRU may include a receive (Rx) coil. In typical wireless power transfer systems, the transmit coil creates an alternating electromagnetic field and the receive coil takes power from the electromagnetic field and converts it back into electrical current to charge the battery and/or power the device.
Inductive charging and magnetic resonance charging are two techniques for wireless power transfer. In inductive charging, the transmit and receive coils are tightly coupled and operate like two windings of a transformer. Most of the energy transfer is via non-radiative near-field electromagnetic waves. In inductive charging, power can be wirelessly transferred over a large range of frequencies, and the resonant frequency at which power is transferred is based on the load impedance.
In magnetic resonance charging, the transmit and receive coils are loosely coupled, which enables a single transmit coil to be used to transmit power to two or more receive coils. The energy transfer in magnetic resonance charging can occur via radiative far-field electromagnetic waves. Unlike inductive charging, the transmit and receive coils used in magnetic resonance charging are tuned to the same resonant frequency to improve the energy transfer efficiency.
The same numbers are used throughout the disclosure and the figures to reference like components and features. Numbers in the 100 series refer to features originally found in FIG. 1; numbers in the 200 series refer to features originally found in FIG. 2; and so on.